Method of sampling well fluids



Sept.' 2, 1958 D. F. BLooM METHOD oF SAMPLING WELL vFLUIDS I2 Sheets-Sheet 1 Filed March ll, 1957 INVENTOR. azaii wo/v i m f n Sept. 2, 1958 D. F. BLOOM 2,850,097

METHOD oF SAMPLING WELLHFLUIDS: Filed March 11, l1957 2 sheets-sheet 2 INVENTOR. DOLORES F. BLOOM ATTORNEY 2,850,097 METHUD GF SAMPLENG WELL FLUIDS Dolores Floyd Bloom, Bakersfield, Calif., assigner to Aircushion Patents @oi-poration, Bakersiieid, Calif., a corporation of California Appiication March l1, 1957, Serial No. 645,373 7 Claims. (Cl. 16o- 3) My invention relates to a new and improved method of sampling well liuids, and more 'particularly toa new and improved method of sampling well iluids or, as it is commonly called, formation testing, yielded by a particular geological strata or formation which has been penetrated by a, drilled well..

arent fice trollable flow o-f gas or oil. The use of a flow bean in the f tester to restrict the ow, and the use of water or drilling This application is a continuation-impart of Vmy prior application for United States Letters Patent filed May 18, 1954, under Serial No. 430,475, now abandoned.

A variety of techniques and of special tools called formation testers have been developed in the petroleum industry forl securing samples of the fluid contained in a given formation which has been penetrated by a well, without requiring the running and cementingof casing and without hailing or otherwise removing the drilling fluid from the well. Such techniques and tools are also utilized in testing the effectiveness of water shut-offsy and may Ibe used to determine whether casing perforations are freely admitting uid from the formation.

As described by Uren in Petroleum f Production Engineering-Oil Field Development, 3rd edition, 1941, such formation testers are employed in conjunction with a packer which, when properly` seated against the wall of the well or casing, relieves the test interval immediately below the packer of the hydrostatic pressure of .the overlying column of drilling fluid inthe well. In straddle testing, above the ybottom of a well, a second packer is employed which is located below the tester. By means of a valve located in the formation tester, fluid is permitted to flow from the formation below the packer, through the tester into a pipe string such as, for instance, drill pipe. Fluid so entering the pipe string is trapped' therein by means of a valve located in the tester, so that the entrapped fluid may be withdrawn from the well with the pipe string for subsequent examination; or if the formation pressure is sufcient to cause the flow of the fluid from the formation to the surface, asustained flow test n through the pipe string will provide, in addition tothe sample, a quantitative measure of the productive capacity of the formation being tested. However, one objection to this method of testing a formation is that there is no control permitted of the rate of the escapement of the fluid and pressure from the formation into the pipe string because of the differential in pressure between the high rock pressure below the packer and the low pressure in the pipe string. Frequently this causes caving or collapsing of the hole immediately below` the packer, thereby causing the packer and the pipe string to which it is attached to stick in the hole.

A specific example of one form 'of formation tester in which the valving means are actuated by a weight, or go-devil, dropped from the surface through the drill pipe, is described by Uren at pages 562-3; but other types of formation testers, such as the Halliburton Hydrospring tester are also in general use, which provide for control of the valve by relative movement between the pipe string and the body of the tester. Either of these testers is typical of a formation tester which may be used uid inthe pipe string to balance the formation pressure have been among the expedients used in testing such formations. A sufficiently restricted ilow bean may be veasily clogged. Counter pressure created vby water or drilling fluid, either alone or accompanied by conventional 'swabbing can never be sufficiently accurately controlled to avoid the risk of either a dry run if the weight of the column of uid is excessive, or of formation damage and cavitation accompanied by apos'sible blowout if -it is insufficient. v 1

My invention provides a method of sampling well fluids which avoids dry runs while at the same time controls the ow of 'fluids into thetester rvand pipe'string in such a manner as to preventcaving of the formation, and insures against blowouts. This is accomplished, in summary, by running a pipe string carrying a formation tester, associated valve means, and apacker into the hole with the valve closed, by introducing gas under pressure into the pipe string, prior to opening the valve, to a pressure approaching but lpreferably below the estimated pressure of the fluid present in the packed off formation to be tested, holdingythe pressure on the well until the formation pressure.. and the pipe pressure are in equilibrium, and l subsequently gradually bleeding off the gas pressure at the surface of theground at such a 'rate as to control the rate of ingress of fluidsV into the tester and pipe string within desired limits and suiciently slowly so as to prevent caving or channeling of the formation below the packer. Gas pressure within the pipe string lower than the pressure in the formation ,-will not result in a blowout because, as the fluid or gas from the formation rises in the pipe string and the fluid or gas ows into the pipe string, the cushion of gas above the valve will compress until the pressure in the pipe string becomes balanced against the formation pressure. Since this compression of the gas in the pipe string cushions the rising uids originating in the formation, shock effects which might precipitate caving or channeling of trie formation are simultaneously avoided.

The manner in which this is accomplished will be best understood from the following description of examples of my method, reference being had to the accompany drawings in which:

Figure l Shows a diagrammatic iliustration of a petroleum well and an example of apparatus useful in carrying out the steps of the method embodied in my invention;

Figure 2 shows a bank of high pressure cylinders, which is preferably used as a source of high pressure gas supply embodied within my invention; and

Figure 3 shows a view of the packer and valve which may be used in practicing this method.

In Figure l there is illustrated diagrammatically a well liti which has penetrated the formation to be testedv l1. As illustrated, the well is provided with a conventional surface casing 12 and a deep string of casing i3.

At the surface of the ground a well cellar l5 is provided, through which the casing i3 rises; a master control valve i6 being provided for the purpose of closing the space between the drill pipe and the casing i3, while a conventional blowout preventer 17 is provided for the same purpose above the master control valve. The casing i3 is clo-sed at its top by a packing gland 20 through which the drill pipe 2l is passed, as shown, and connected to the casing 13 at the gland 20 is a conventional drilling rotary table 27 through which the drill pipe 2l likewisel extends. A conventional valve assembly, also known as a Christmas tree, 45 having cross T 46, a pressure gauge 47, a bleed valve 48 and a connection 49 is provided, as shown. All of the foregoing apparatus is conventional in rotary drilling operations and forms no part of this invention. On the top of the Christmas tree 45 there is provided a twoway cock valve 60 connected on one side to valve 42 by means of a suitable length of pipe 43. A high pressure source of gas 4t) is connected to the valve 42 by means of pipe 41. Compressor 50 is likewise connected to valve 60 by means of connections 51 and 53 separated by valve 52.

When fluid is to be sampled from the bottom of a well, a rathole 30, which is a portion of the well of reduced diameter, may be drilled at the bottom of the well to provide an annular shoulder31 against which a suitable packer 32 can seat for the purpose of relieving the formation to be tested from the weight of the drilling and other fluid in the hole. For a detailed showing of the `packer 32, attention is invited to Figure 3, which will be described in detail later. After the drilling of the ratholc 3d, the drill pipe is withdrawn from the hole and the packer 32 is attached to the end of the drill pipe or other pipe string. The tester 33 is provided with a positive seating valve 34. The valve 34 may be of any type desired as long as it provides a hydraulic-tight seat inside the packer. As has been pointed out above, the valve 34 can-be either of a type in which a go-devil" or ball is dropped through the casing to open the `same or may be of the type which contains a J-tool which opens or closes the valve 34 by a partial rotation of the pipe string. Inasmuch as the particular type of valve 34 which is used forms no part of this invention, a further detailed description thereof is deemed unnecessary. `A tester intake pipe, which extends below the packer 32 into the formation being tested, is provided as shown.

After the packer 32 and tester 33 with the valve 34 has been attached to the pipe string, and with the valve 34 closed so that no uid remaining within the hole can enter into the pipe string, the pipe string is lowered into the well. The packer may be set on the shoulder 31 either at this time or at a later time, if the tester Valve is controlled by downward pressure on the pipe string. At this time the method of the present invention contemplates a departure from the conventional practices which have thus far been referred to.

The pressure of the fluid present in the formation to be tested 11 being estimated or approximately computed by known methods, I now create within the pipe string 21 a gas pressure as nearly approximately equal to the formation or rock pressure as possible. The precise pressure of the gas in the drill pipe varies according to conditions from well to well. It has been found in actual practice that preferably this pressure should be less than the formation pressure, but under certain circumstances it may be desirable to go above this formation pressure, and the best results have been obtained when a pressure approximately equal to the formation pressure is used. On the other hand, pressures ranging from formation pressure down to approximately one fifth of the formation pressure could be used without departing from the spirit of my invention, and with varying degrees of satisfactory results. This is done by forcing air or inert gas, such as nitrogen, into the pipe string 21 at the surface of the ground until the desired pressure is built up. The use of an inert gas is preferred because it cuts to a minimum the re hazard present at the well head and even within the well itself. Nitrogen, an inert gas, is particularly desired because of its chemical inertness in reference to gases present in earth formations, giving a much better formation gas sample at the casing head.

The derrick substructure 25 supports Since the tester 33 and pipe string 2l are lowered into the well 10 with the valve 34 is a closed position, it will be obvious that the inside of the pipe string 21, after it reaches the level of the formation to be tested, is free of drilling mud which might otherwise enter from the out side of said pipe 21. i

As illustrated in Figure 1 the gas may be supplied either by the compressor 50 or by other high pressure source 40, such as a bank of storage tanks, which is shown in detail in Figure 2, or they may both be used. The storage tanks 40 preferably consist of a plurality of tanks 140 attached to a header 141 with a manifold 142 connected thereto. Provided in the header 141 is a plurality of valves 143. As can be seen from a study of Figure 2, the header 141 will permit the admission of gas from any bank of bottles into the manifold 142 as desired. For example, a single bank of bottles can be opened at one time or any combination or all of the bottles can be opened at one time, depending upon the quantity and gas pressure desired to be introduced into the well. The purpose of this arrangement is to permit a more accurate control of the quantity and pressure of gas introduced into the pipe string.

An arrangement for opening the tester valve by dropping a weight while maintaining the pipe string 21 closed at its upper end may be provided as, for example, in Patent No. 2,137,296, dated November 22, 1938, to Macready; but where a tester such as the Halliburton Hydrospring tester previously referred to is employed,

lthe valving means in the tester may be opened by relative movement between the pipe string 21 and the body of the tester 33, accomplished by permitting the Weight of the pipe string to bear -against the tester, thus seating it firmly on the shoulder 31 at the top of the rathole 30. and then backing off a half or quarter turn on the pipe string. In other types of testers mere downward pressure on the pipe string sets the packer and causes opening of the tester valve a few minutes later. `It is immaterial` so far Ias the present invention is concerned when the packer is set, so long as it is set before the tester valve is opened.

When the valve 34 within the tester 33 -is opened, the resulting changes `of pressure within the pipe string 21 are noted on the gauge 47. If the pressure within the pipe string 21 should be indicated to be falling after the opening of valve 34, this indicates that the pressure introduced into the pipe string 21 was greater than the pressure in the formation to be tested, which in turn will indicate that pressure is backing up from the pipe string into the formation, a condition which, except in special situations, is undesired. When this condition is found to exist, the valve 48 is opened to bleed off the pressure in the well sufficiently 4to bring the pipe pressure above the packer into equilibrium with the formation pressure. Such a state of equilibrium will be indicated on the gauge 47 when it stabilizes or ceases to rise or fall.

The converse is true if it is found that the pressure in Ilthe pipe string 21 rises sharply and rapidly when the valve 34 is opened. This will be an indication that the pressure in the pipe is lower than that of the formation to be tested. When this condition is found to exist, the valve 48 is maintained closed until the formation pressure and the pipe pressure achieve equilibrium, which is indicated in the same way described above.

After the stabilization of the pressure within the pipe p 21 has been attained, whichever condition has been found to exist, `the valve 48 is opened gradually and the pressure r in the pipe 21 is slowly reduced to permit the slow and formation to be tested.

The gradual reduction of pressure within said pipe 21, yachieved by employing the bleed valve 48 as a throttle,

as described, forms an important feature of the present invention, since by this practice the rate of flow of fluid from the formation 11 into the tester'33 and thence up into the pipe 21 can be held as low as desired, Without the use of a flow bean which might clog; and, as pointed out above, possible caving or channeling of the formation is prevented by means of this gas cushion.

It is to be here noted that, if the formation pressure is sufficient, after the opening of the valve 48 and the bleeding off of the pipe 21, the well can be flowed through the bleed-off valve 4S if desired or the test can be stopped before the well begins to flow and the specimen desired to be taken is entrapped within the pipe 21 by closing the valve 34 and then coming out of the hole with the pipe 21.

In c-ases in which exceedingly high formational pressures are expected to be encountered during the making of a formation test, it is sometimes desirable to su-pple-l ment the gas pressure cushion employed in the method embodied in the present invention with a liquid, preferably water, but occasionally by the use of drilling mud which is heavier in specific gravity and therefore can hold a much higher formation,- or bottom hole, pressure. When it is desired to proceed in this manner, the w-ater or specially prepared drilling mud having the specific gravity desired is gravitied into the open pipe 21 as it is run into the hole. In this Way the exact height and weight of the liquid introduced can be measured. For example, if it is desired to include a column of liquid in the pipe 500 feet high, this liquid is introduced into the open pipe when 500 feet of pipe have been run and the remainder of the st-ring is run into the 4hole dry. After the pipe is run, with the column of liquid therein, the gas line valve 42 is opened and gas is introduced through the pipe 43 into the pipe 2li in the same manner as described above. Gas yfrom the reservoir 40 thus provides, above the liquid, a gas cushion such that the total pressure exerted at the tester valve by the combination liquid and gas equals the pressure desired to be exerted on the formation to be tested. At this point the process described above is repeated, the valve 42 is closed, -and the valving means in the tester is opened with the packer set, :as previously described, and the method of the present invention -is then continued on from this point in the same manner as previously described.

Where such a combined liquid-gas cushion is employed, it is important that the pressure exerted at the tester valve 34 by the liquid be substantially less than the pressure of the formation to be tested and that a substantial part of the cushion be compressed gas. Under all circumstances a suflicient amount of compressed gas must be used above the wa-ter or mud to insure against the liquid cushion being forced against the top of the Christmas tree as a water hammer regardless of the formation pressure encountered.

It is to be understood that variations in packers, valves and the like can be resorted to; that the hole can be cased or open and other modifications and changes made without departing from the spirit of my invention, which is set forth in the appended claims.

1 claim:

1. The method of testing a formation penetrated by a Well comprising the steps of providing a conduit having a valved tester and a packer at the lower end thereof, maintaining said conduit and tester sealed from fluids present in said well until said packer is set, pressurizing said conduit and tester by introducing gas under pressure therein, maintaining the pressure within said conduit above said tester in the range of from approximately onefth of the pressure in the formation to be tested to approximate equality with the pressure in the formation to be tested, setting said packer while said conduit and tester are sealed to remove the hydrostatic pressure of overlying fluid in said well from the formation to be tested, providing an opening in said tester, when said packer is set, to permit the flow of a fluid therethrough from the formation being tested into said tester and conduit, and gradually releasing the gas pressure within said conduit and tester to permit a gradual rise, through the opening provided in said tester, into said conduit of the fluid from the formation being tested entrapped below said packer, in an uncontaminated condition.

2. A method according to claim l in which the pressure in said conduit above said tester is maintained at approximately one-fifth the pressure in the formation to be tested.

3. A method according to claim 1 in which the pressure in said conduit above said tester is maintained at approximate equality with the pressure in the formation to be tested.

4. A method according to claim 1 in which the gas under pressure introduced into said conduit above said tester is an inert gas.

5. The method of testing a formation penetrated by a well comprising the steps of providing a conduit having a valved tester and a packer at the lower end thereof, maintaining said conduit and ltester sealed from fluids present in said Well until said packer is set, pressurizing said conduit and tester by introducing gas under pressure therein, maintaining the pressure within said conduit above said tester in the range of from approximately oneflfth of the pressure in the formation to be tested to approximate equality with the pressure in the formation to be tested, setting said packer while said conduit and tester are sealed to remove the hydrostatic pressure of overlying fluid in said well from the formation to be tested, providing an opening in said tester, when said packer is set, to permit the flow of a uid therethrough from the formation being tested into said tester aud conduit, bringing to equilibrium the gas pressure in said conduit and the pressure in the formation being tested and gradually releasing the gas pressure within said conduit and tester to permit a gradual rise, through the opening provided in said tester, into said conduit of the fluid from the formation being tested entrapped below said packer, in an uncontaminated condition.

6. The method of testing a formation penetrated by a well comprising the steps of providing a conduit having a valved tester and a packer at the lower end thereof, maintaining said conduit and tester sealed from fluids present in said well until said packer is set, pressurizing said conduit and tester by introducing a liquid into said conduit in a quantity sufficient only to provide a pressure at said tester valve substantially less than the pressure of the formation to be tested and by introducing gas under pressure into said conduit, maintaining the total pressure within said conduit above said tester provided by said liquid and gas in the range of from approximately one-fifth of the pressure of the formation to be tested to approximate equality with the pressure in the formation to be tested, setting said packer while said conduit and tester are sealed to remove the hydrostatic pressure of overlying fluid in said Well from the formation to be tested, providing an opening in said tester, when said packer is set, to permit the flow of a fluid therethrough from the formation being tested into said tester and conduit7 and gradually releasing the gas pressure within said conduit and tester to permit a gradual rise, through the opening provided in said tester, into said conduit of the fluid from the formation being tested entrapped below said packer, in an uncontaminated condition.

7. A method according to claim 6 in which the total pressure in said conduit and tester provided by said liquid and gas is brought into equilibrium with the pressure in the formation being tested immediately prior to gradually releasing the gas pressure within said conduit above said tester.

References Cited in the file of this patent UNITED STATES PATENTS 

